Our current pattern seen from Black’s side. The elements differ only a little in their details. The first point: Black has a capture he wants to make in RxR. The second point: RxR also would check White’s king. The third point: White’s rook is protected by his queen. The fourth point: Black can attack White’s queen with protection, and while also attacking a loose White piece, with Qc6. White could just move his queen to e2 and still protect his rook on d1; but then he loses the rook on b5, which Black has forked. (It goes 1. …Qc6; 2. Qe2, RxR+; 3. QxRd1, QxRb5.)
So in reply to 1. …Qc6, suppose White plays 2. QxQ. Now Black does not recapture White’s queen. He knows that if he first plays other moves with check, White’s queen still will be there to take afterwards. Thus Black plays 2. …RxR+—and after White moves his king, Black has 3. …b7xQ, netting a rook.
What if Black instead bites after 2. QxQ by playing 2. …b7xQ? Notice that now White is in a minor fix because both of his rooks are under attack (the pawn capture of Black’s queen just happened to create a threat against the rook on b5). This doesn’t mean White has to lose anything; he simply plays 3. RxR, permitting Black to play c6xR and now both sides have traded queens and rooks. The key point, however, is that if Black does play 2. …b7xQ, giving White a move to use to save his rook on d1, White mustn't squander it by playing 3. Rf1. That's a superficially appealing move because now his rook has some protection, but in fact it's ruinous because White has forfeited the initiative, enabling Black to play 3. …RxR+, 4. KxR, c6xR—and again Black has won a rook. The lesson, of course, is that if two of your pieces are threatened at once, try to do some damage with one of them. That is what White does in this variation by playing 3. RxR instead of the cowardly 3. Rf1.
Assuming White sees all this, what will he do? He will reply to 1. ...Qc6 with RxR, permitting Black to play QxQ; this way White gives up a queen for a rook, which isn’t quite as bad as giving up a rook outright (though the game pretty well is over either way).